I don't know how to help my friend

Hi everyone this is gonna be a long post, sorry. So one of my closest friends has been in an emotionally abusive relationship for a long time and has a 1 year old with the guy. A few months ago she called me crying saying he had beat her up and she needed to leave. So I rushed over there to help her. She had awful bruises all over her body. The guy had been arrested but was expected to be released very soon so we packed her and her sons stuff quickly and left. Her and her son came to stay at my house while our other friend took her dog. So a few days go by, she's getting on her feet, figuring out a job situation and daycare for her son when she decided to meet with the boyfriend. They met with family to mediate and worked out a coustody schedule in which he would have the kid for the weekend. So the next day is Saturday so I go with her to drop off the kid and he has literally thrown away all her stuff and was just generally being a dick. So we drop the kid off and go and she says she wants to go out that night because she hasn't been out since before she was pregnant. I agree to be the DD. So we go out and she gets blackout drunk (she didn't seem that drunk but now thinking back she probly had a really low tolerance). But that's fine, she's been stressed. So the night ends and I drive her home. She tells me she needs to go out to the car to get her phone so I give her the keys (I know, I'm so mad at myself for thinking that was ok). A few mins later I think hmm she's been gone for awhile so I thought maybe she fell down or something. So I go out and the cars gone. I immediately call my friends and drive to the boyfriends house and she's there, BREASTFEEDING the baby while blackout drunk and naked. We somehow convince her to go outside but after that she wouldn't leave with us and the boyfriend kept coming out yelling at us and telling her to stay. At this point it's like 4 am and he convinced her to go back inside so we just leave cuz we didn't know what to do. We don't hear from her and her phone was at my house for 2 days then she just shows up at my house. She was so upset with herself and swore she's never go back to him or do something like that again. So I go to work and when I come back all her stuff is gone. Since then it's been like 2 months and I've tried to get in contact with her but her Facebook is deleted and her phone has been shut off... I contacted her family and they haven't heard from her since November. I'm worried about her and her son and I don't know what to do. I've considered going to her house or calling the cops but I don't know what the right choice is or if I can even help at all... does anyone have any advice?